Exogenic Processes: Denudation, Weathering, Mass Movements, Erosion, Transportation, Deposition
Geography › Geomorphic Processes and Landform Evolution · Topic 3.13
Exogenic processes are the surface processes that wear down the land. Denudation, meaning the stripping of the surface, is the combined result of weathering (the in-place breakdown of rock), mass movement (the downslope movement of weathered material under gravity), erosion (the removal of material by moving agents), transportation (carrying it away) and deposition (laying it down). The agents are running water, groundwater, glaciers, wind and waves, and their work leads to landforms of erosion and deposition.
5 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution
At a Glance
- Denudation Stripping of the land surface
- Steps Weathering, mass movement, erosion, transport, deposition
- Agents Water, wind, ice, waves
- Energy Sun and gravity
- Cycle of erosion Proposed by W. M. Davis, 1899
- Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution
Where Does It Fit?
This topic continues from the endogenic processes and sets out the whole chain of surface processes. It then leads into the detailed topics on weathering, mass movements and the landforms made by each agent. Previous topic: Endogenic Processes: Diastrophism, Orogenic and Epeirogenic Processes. Next topic: Weathering: Chemical, Physical/Mechanical and Biological Processes.
What Are Exogenic Processes and Denudation?
In short: exogenic processes are the surface forces that wear down what endogenic forces build.
Exogenic processes take their energy from the Sun and from gravity. The Sun provides heat that drives the atmosphere and the water cycle, and gravity pulls material downslope. The action of these forces in lowering and levelling the land is called denudation, which literally means stripping off. The aim of the processes is to bring the surface to a common level, called gradation. Denudation has four parts: weathering, mass movement or wasting, erosion and transportation. The agents of erosion and transport are running water, groundwater, glaciers, wind and waves. These processes are examined in Soil Erosion and Conservation and in the topics on landforms that follow in this subject.
What Are the Steps from Rock to Landform?
| Step | Meaning | Key point |
|---|---|---|
| Weathering | Breaking and decay of rock in place | No movement of material; see Weathering: Chemical, Physical/Mechanical and Biological Processes |
| Mass movement | Downslope movement of weathered debris under gravity | Gravity is the force; see Mass Movements: Heave, Flow, Slide; Slow, Rapid and Landslide Categories |
| Erosion | Removal of material by a moving agent such as water, wind or ice | Needs a moving agent |
| Transportation | Carrying the material | By solution, suspension, saltation, traction and sliding |
| Deposition | Laying down the material when the agent loses energy | Forms plains, deltas, dunes, moraines |
Weathering is a preparation for erosion, since loosened rock is easier to carry. The difference between weathering and erosion is that weathering takes place without any agent moving the material, while erosion needs one.
Who Are the Agents and How Do They Move Material?
- Running water: the most important agent in most regions. It moves material as dissolved load, suspended load and bed load.
- Wind: lifts fine sand and dust (deflation), blasts rock with sand (abrasion) and drops the load in dunes and loess sheets.
- Glaciers: pluck and grind rock, and carry a mixed load of boulders and clay.
- Waves and currents: cut cliffs and move sand along the shore (longshore drift).
- Groundwater: dissolves limestone and builds caves.
Each agent deposits its load when its energy falls, for example when a river enters the sea or the wind drops. The landforms of each are in the topics that follow.
What Is the Cycle of Erosion?
The American geographer William Morris Davis proposed the geographical cycle, also called the cycle of erosion, in 1899. He suggested that a land uplifted rapidly is then worn down by rivers through a regular sequence of stages, if there is no further uplift, as structure, process and time determine the landscape.
| Stage | Features |
|---|---|
| Youth | Upland with steep, V-shaped valleys, rapids, waterfalls, and broad flat interfluves; vertical erosion |
| Maturity | Maximum relief; well-developed streams, gentle valley floors and meanders; rounded hills |
| Old age | Very gentle slopes, wide floodplains and meanders; the land is reduced to a nearly flat surface, the peneplain, with occasional resistant hills called monadnocks |
Davis described a cycle that could be interrupted by renewed uplift, called rejuvenation, which produces features such as river terraces and incised meanders. Later geomorphologists criticised the theory. Walther Penck in the 1920s argued that uplift and erosion occur at the same time, and that slopes retreat parallel to themselves, and L. C. King’s pediplanation theory, based on arid and semi-arid landscapes of Africa, stressed parallel retreat of slopes leading to extensive plains called pediplains. As an analytical point, Davis’s model is now seen as an idealised teaching framework, but its vocabulary of youth, maturity and old age remains useful for describing landscapes.
Why Is This Topic Important?
- Sequence Order of steps is asked
- Terms Weathering versus erosion
- Model Davis’s cycle
What Came Next?
The next topic explains the three kinds of weathering in detail. Next topic: Weathering: Chemical, Physical/Mechanical and Biological Processes.
Key People and Terms
- Denudation Stripping of the land
- Erosion Removal by a moving agent
- Deflation Lifting of loose material by wind
- Abrasion Grinding by the load carried
- Peneplain Almost-plain, final stage of Davis’s cycle
- Saltation Bouncing of grains along the bed
Exam Corner
Points to Remember
- Weathering needs no agent; erosion needs one.
- Mass movement is driven by gravity.
- Davis proposed the cycle of erosion in 1899.
- Davis’s stages: youth, maturity, old age.
- Deposition occurs when the agent loses energy.
Do Not Confuse With
- Weathering and erosion In-place breakdown versus removal
- Denudation and erosion Total stripping versus one part of it
- Davis and Penck Down-wearing cycle versus slope retreat
Memory Hook
Weather, slide, erode, move, deposit: five steps in a row.
Mains Angle
Questions ask for the sequence of surface processes. These points add depth.
- Sequence Five steps
- Agents Five agents
- Models Davis, Penck and King
A Question You May Face
An original practice question, not a past paper question.
“Explain the sequence of exogenic processes and the role of the different geomorphic agents in shaping the land.”
How to Answer
- Define Denudation.
- Sequence Five steps.
- Agents Water, wind, ice, waves.
- Model Cycle of erosion.
GS Relevance
Frequently Asked Questions
What is denudation?
Denudation is the wearing down and lowering of the land surface by exogenic processes. It consists of weathering, mass movement, erosion and transportation, and its agents are running water, groundwater, glaciers, wind and waves, driven by solar energy and gravity.
What is the difference between weathering and erosion?
Weathering is the breakdown of rock in place, with little or no movement of the broken material. Erosion is the removal and transport of that material by agents such as water, ice, wind and waves, so it involves movement.
What is mass movement?
Mass movement is the downslope movement of rock, soil and debris under the force of gravity, with no flowing agent such as a river. It ranges from slow creep to sudden landslides and rockfalls, and it is encouraged by steep slopes and heavy rainfall.
What is Davis's cycle of erosion?
The cycle of erosion proposed by William Morris Davis in 1899 describes the evolution of a landscape after uplift through youth, maturity and old age. The end stage is a nearly flat peneplain with occasional resistant hills called monadnocks.
What are the main agents of erosion?
The main agents of erosion are running water, glaciers, wind, waves and groundwater. Each picks up and carries material when it has energy and deposits it when its energy falls. Running water is the most widespread agent, while wind is important in deserts and glaciers in cold highlands.
PYQ Practice — Statement Analysis
1 Weathering involves the transport of broken rock by an agent.
That is erosion.
2 Gravity is the force behind mass movement.
No transporting agent is needed.
3 The cycle of erosion was proposed by W. M. Davis.
He proposed it in 1899.
4 A peneplain is the youthful stage of the cycle of erosion.
It is the end stage of old age.
Past Mains Questions on This Topic
This topic comes under Geomorphic Processes and Landform Evolution. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
Related Topics
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